Systems for generation of x-ray radiation are used, for example, in medical diagnostics in order to acquire radiographic images or to produce planar images for technical diagnostic applications. One further effective use of x-ray radiation is in the treatment of substances to reduce the impact of biological and other contamination. For example, food can be irradiated to prolong useful life, making the food safer to consume. Waste water or runoff may be irradiated in the same manner to reduce the effects of contamination.
In the field of technical diagnostic imaging, x-rays are especially effective at penetrating internal structures of a solid object to be examined, and the images formed by the x-rays that pass there through reveal internal flaws or structural defects of the object. Technical diagnostic x-ray imaging thus provides a valuable quality control inspection tool for evaluating structural aspects of a product during manufacture and over the useful life of the product. This form of diagnostic analysis is sometimes advantageous over other types of evaluation, since the imaging object need not be destroyed in the process of the evaluation. For this reason, technical diagnostic imaging is also known as non-destructive testing.
A typical prior-art arrangement is schematically illustrated in FIG. 1a. An x-ray tube, 1, typically comprises an electron gun having a cathode (not shown) that emits a beam of electrons, 2, that are accelerated to an anode 3. The anode is comprised of a metal target surface, such as tungsten, from which x-rays, 4, are generated due to the impact of the accelerated electrons. The radiation is composed of two parts, bremsstrahlung and characteristic radiation. Bremsstrahlung is the major part and is radiated with an intensity profile that has its maximum perpendicular to the linear path of the electron beam, 2, and has a distribution proportional to the angel by sin2 (v) (where v=0 is the angle parallel to the electron linear motion i.e. the bremsstrahlung radiation intensity maximum is perpendicular to the electron beam path, 2), while the characteristic radiation has a uniform intensity distribution over a full solid angle (spherical). A sin 2 distribution 10 is shown in FIG. 1b, where the radial bremsstrahlung intensity from the electron path is shown to be uniform. Accordingly, and as can bee seen from FIG. 1a, the anode 3 is commonly placed at an angle to the axis of the electron beam, 2, the x-rays, 4, may be transmitted in a direction generally perpendicular to the electron beam axis. It should be noted that roughly half of the generated x-rays will penetrate into the anode in this arrangement and this will be absorbed. The x-rays, 4, may then be passed through a thin beryllium window 5 used to collimate the x-ray beam and also provide a vacuum seal within the x-ray tube 1. Thereafter, the x-rays 4 exit the x-ray tube 1 along a generally conical path where the apex of the cone is roughly coincident with the spot on target formed by the impinging electron beam.
This divergent radiation pattern, originating essentially from a point source will have an intensity fall off in vacuum, proportional to the inverse square of the distance r, i.e. 1/r2 for pure geometrical reasons. To effectively employ this radiation pattern at proper doses, radiation doses accounting for the fall off with distance, must be generated, and the object of interest must be positioned properly in the radiation cone. Although some radiation sources use multiple point sources, or one or more mobile point sources, to make up for the suboptimal emission pattern, such systems have their own inherent drawbacks and complexities. In particular, complications involving source timing, positioning, etc. are commonplace
In the treating of materials for decontamination or sanitation purposes in particular, it is important to be able to deliver a sufficiently uniform and sufficiently strong radiation pattern so as to ensure adequate radiation to reduce the impact of microorganisms (or larger organisms) and contaminants.
One approach has been made to solve the above mentioned problems by the introduction of a large area flat panel source for x-ray generation. An example of such an implementation is disclosed in EP1948249, in which the one or more large area flat panel sources of x-ray radiation are directed into a target zone. A target substance to be treated is placed within the target zone, such as via conveyor belt, pipe, etc., and is irradiated with radiation from the one or more flat panel sources to reduce the biological effects of the contaminant presence in the target substance. A drawback with this solution is the distribution of the intensity where a large portion is lost as it is transmitted parallel or close to parallel to the surface. FIG. 2 conceptually illustrates the x-ray distribution in a prior art flat panel x-ray arrangement 20, comprising a transmissive cathode 22 and an anode 24, also indicating the parallel x-ray distribution as mentioned above.
There is therefore a need for an improved x-ray source and corresponding system that at least alleviates the prior art reliability problems, with further focus on low cost applications.